RX300 1999

Intake Air Temperature Sensor

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Operation



Specific to:

Lexus RX300 1999-2003

Lexus RX330 2004-2006

The Intake Air Temperature (IAT) Sensor is a Negative Temperature Coefficient (NTC) Thermistor that monitors the intake air temperature. The IAT Sensor operates within a 5 volt DC reference range, and provides a linear input signal to the Powertrain Control Module (PCM) that is based upon the measured engine intake air temperature. The PCM uses data from the IAT Sensor to calculate Air-Fuel mixture, ignition timing, and fuel injector pulse width. The IAT Sensor is integrated with the Mass Air Flow (MAF) Sensor as a physical component.

Removal & Installation



Specific to:

Lexus RX300 1999-2003

  1. Before servicing the vehicle, refer to the Precautions Section.
    NOTE
    If working near and/or around the SRS system and components, be sure to disable the SRS system.

  2.  
  3. Disconnect the negative battery cable.
    NOTE
    When disconnecting the cable be sure that the ignition switch and headlight switches are off.


    NOTE
    When disconnecting the cable, certain systems will have to be initialized after reconnecting the cable. These systems are adaptive front lighting system, power window control system, power back door system, SRS system, audio system, sliding roof system and certain DTC codes. Be sure to write down any important information before disconnecting the cable. The Toyota scan tool, or equivalent, must be used. Follow the directions on the appropriate scan tool to complete initialization procedure.

  4.  
  5. Disconnect the IAT/MAF meter connector.
  6.  
  7. Remove the retaining screws.
  8.  
  9. Remove the component from its mounting.
  10.  
  11. Discard the gasket.

    Click image to see an enlarged view

    Fig. IAT/MAF sensor and related components-RX300

  12.  

To install:


NOTE
Be sure to use new fasteners, as required.

  1. Installation is the reverse of the removal procedure.
  2.  
  3. Be sure to use a new gasket.
  4.  

Testing



IAT Circuit Testing

Specific to:

Lexus RX300 1999-2003

Lexus RX330 2004-2006

Use a suitable scan tool, a Graphing Multi-Meter (GMM), or a Digital Volt-Ohm Meter (DVOM) in order to view the IAT data.

IAT Sensor logic is relative to the scale of resistance: when the intake air temperature is low, the voltage is increased. When the coolant temperature is high, the voltage is decreased .

Inspect the air intake tube, the engine air filter, and the MAF and/or IAT sensors for contamination and physical damage in order to verify that the air induction system is in proper working order. If an air induction system fault is evident, repair as required before continuing.

If a DVOM is being used, additional information may be acquired by taking measurements at the sensor connector as well as the PCM connector. If a significant voltage drop is measured (greater than 0.5 volts DC), check the wiring harness and connections for corrosion, poor pin connections, or damaged wires.

If all engine wiring and pin connections are confirmed, disconnect the IAT Sensor to verify the signal with a DVOM, and verify PCM communication before replacing the IAT Sensor.

Click image to see an enlarged view

Fig. IAT Sensor Range Chart

IAT Sensor Strategy

Specific to:

Lexus RX300 1999-2003

Lexus RX330 2004-2006

The IAT Sensor provides a linear input signal to the Powertrain Control Module (PCM) for a number of engine control system calculations. The IAT signal is compared with Manifold Absolute Pressure (MAP), Mass Air Flow (MAF), Engine Coolant Temperature (ECT), and Fuel Trim (HO2S) in order to determine the correct Air-Fuel mixture for measured operating conditions.

Related Diagnostic Trouble Codes

Specific to:

Lexus RX300 1999-2003

Lexus RX330 2004-2006



Click image to see an enlarged view

Fig. Related Diagnostic Trouble Codes

 
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